EXISTS 在SQL語句中怎么用？

EXISTS
指定一個子查詢，檢測行的存在。
馬克- to-win：馬克 java社區(qū)：防盜版實名手機尾號： 73203。
SELECT DISTINCT name
FROM student
WHERE EXISTS
(SELECT *
FROM register
WHERE id = student.id);

(note that if some rows in student register.id =student.id, all those rows in student are selected out.)